There are only a few common ICs used in inverter drive circuits. Imagine that the general circuitry of an inverter consists of a main circuit (including a three-phase rectifier circuit and a three-phase inverter circuit) and a drive circuit. Even inverters with different power levels often use the same type of drive IC, and their structures and layouts are very similar.
Early and low-power frequency inverters often used TLP250 and A3120 (HCPL3120) driver ICs, which had simple internal circuits and lacked IGBT protection circuits. Later, the combination driver circuit of PC923 and PC929 was widely adopted. Typically, the upper three IGBTs were driven by PC923, while the lower three IGBTs were driven by PC929. PC929 includes IGBT detection and protection circuits. The A316J, a dedicated driver chip with a higher degree of intelligence, was also used in many models.
By becoming familiar with the pin functions of driver ICs and mastering relevant testing methods, one can gain the ability to diagnose and test faults in driver circuits, as well as to replace and repair different models of driver ICs in emergency situations.
I. TLP250 and HCPL3120 driver ICs:
Figure 1 Functional circuit diagrams of three driver ICs
TLP250: Input current threshold 5mA, power supply voltage 10-35V, output current ±0.5A, isolation voltage 2500V, turn-on/turn-off time (tPLH/tPHL) 0.5μs. It can directly drive 50A 1200V IGBT modules and was widely used in low-power inverter drive circuits and early inverter products.
HCNW3120 (A3120): Its internal circuit structure is the same as HCPL3120 and HCPLJ312, but due to differences in materials and manufacturing processes, the latter has lower electrical isolation capabilities than the former. Input current threshold is 2.5mA, power supply voltage is 15-30V, output current is ±2A, isolation voltage is 1414V, and it can directly drive 150A/1200V IGBT modules.
The pin functions of the three driver ICs are basically the same. In low-power models, TLP250 can be used to directly replace the other two HCNW3120 and HCPL3120. In most cases, TLP350 and HCNW3120 can be interchanged. Although their individual parameters and internal circuits are different, such as the lower current output capability of TPL250, in high-power models of frequency converters, the driver IC often has a post-amplifier, so the current output capability of the driver IC is not too picky.
Driver ICs are essentially optocouplers, possessing excellent electrical isolation characteristics. The input-side internal circuitry consists of a single LED, exhibiting distinct forward and reverse resistance characteristics. Using a pointer-type multimeter on the ×1k range, the forward resistance between pins 2 and 3 is approximately 100kΩ, while the reverse resistance is infinite. On the ×10k range, the forward resistance is approximately 25kΩ, and the reverse resistance is also infinite. Naturally, the resistance between pins 2 and 3 and all output pins is infinite. There are also distinct forward and reverse resistances between pins 5 and 6, and between pins 5 and 8. When the red probe is connected to pin 5, the resistance is 10kΩ/30kΩ; when the black probe is connected, the resistance is close to infinity. Due to differences in materials, manufacturing processes, packaging types, and the type of measuring instrument used, the measured values will vary. The TLP250's output circuit uses a complementary voltage follower output circuit, with V1 and V2 being bipolar transistors. The output circuit V2 of the HCPL3120 uses a DMOS transistor, and the output-side resistance values of the two chips differ. During power-on testing, the following conclusions can be drawn from the driver IC's circuit structure: when the input current path at pins 2 and 3 is connected, V1 inside the TPL250 conducts, and the voltage at pins 6 and 7 is close to or equal to that at pin 8; when the input current at pins 2 and 3 is zero, V2 inside the TPL250 conducts, and the voltage at pins 6 and 7 is close to or equal to that at pin 5. This is the basis for judging whether the TLP250 is good or bad.
TLP250 online measurement:
Due to variations in model and the different values of the peripheral circuits, the measured online resistance values are not very meaningful. With the power supply on, the condition of the TLP250 can be easily determined. Live testing of the drive circuit must be performed only after the drive circuit has been inspected separately or after the power supply to the inverter power circuit has been disconnected! It is strictly forbidden to directly measure the drive circuit with the probes while the entire machine is running—interference signals introduced by the probes may accidentally trigger the IBGT, causing serious damage! With the inverter circuit disconnected or its power supply cut off, and the CPU motherboard able to output normal six-channel drive pulses, the operating status of the driver IC can be tested online.
When the inverter's control circuit is in the off state, the voltage between pins 2 and 3 should be 0V, and the voltage between pins 5 and 6 should be 0V. Operate the inverter's operation display panel to put it in the start-up state. The voltage between pins 2 and 3 should have a positive voltage value of approximately 0.6V. At this time, there should be a voltage output of approximately 2-4V between pins 5 and 6. This indicates that the TLP250 is good. If the input voltage at pins 2 and 3 changes, but the output voltage does not change, or the output voltage remains at a fixed high or low level, it indicates that the TLP250 is damaged.
Of course, an external power supply can be connected in series with a current-limiting resistor to provide the input current to the TLP250, and the voltage change at the output pin can be detected to determine whether the TLP250 is good or bad. The above detection method is also applicable to the detection of HCNW3120, etc.
II. PC923 and PC929 driver ICs:
Figure 2 shows the driver ICs for the paired application: PC923 (8 pins) and PC929 (14 pins).
Two driver ICs often appear in pairs, forming a classic combination pattern in driver circuits. The PC923 drives the upper three IGBTs, while the PC929 drives the lower three IGBTs, simultaneously detecting the IGBT on-state voltage drop, providing overcurrent protection for the IGBTs, and outputting an OC alarm signal. The PC929 differs from ordinary driver ICs in that it internally includes IGBT protection circuitry and an OC signal output circuit, integrating driving and protection functions into one unit.
The PC923's specifications are as follows: Input current (IF) 5-20mA, power supply voltage 15-35V, output peak current ±0.4A, isolation voltage 5000V, and turn-on/turn-off time (tPLH/tPHL) 0.5μs. It can directly drive low-power IGBT modules up to 50A/1200V. The PC923's circuit structure is similar to the TLP250, but the output pins are slightly different. A current-limiting resistor can be connected between pins 5 and 8 to limit the output current and protect the internal V1 and V2 transistors. In conventional applications, pins 5 and 8 are directly shorted and connected to the positive terminal of the power supply. With slight modifications to the output leads, it can be interchanged with the TLP520 and A3120. Its power-on detection method is the same as the TLP250 and will not be elaborated here.
The parameters of the PC929 are similar to those of the PC923, but its circuit structure is more complex. Pins 1 and 2 are the cathodes of the internal LED, and pin 3 is the anode. Pins 1 and 3 form the signal input terminals. Pins 4, 5, 6, and 7 are unused terminals. The input signal is isolated by an internal optocoupler and amplifier before being input to the push-pull output circuit via the interface circuit. Pins 10 and 14 are the negative power supply terminals on the output side, pin 13 is the positive power supply terminal on the output side, and pin 12 is the power supply terminal for the output stage. In general applications, pins 13 and 12 are shorted. Pin 11 is the drive signal output terminal, connected to the IGBT or a post-amplifier circuit via a gate resistor. Pin 9 of the PC929 is the IGBT voltage drop signal detection pin. Pins 9 and 10 are connected in parallel to the collector and emitter terminals of the IGBT via an external circuit. The normal voltage drop of the IGBT under rated current is only about 3V. An abnormal voltage drop indicates that the IGBT is operating under a dangerous overcurrent condition. Pin 8 of the PC929 is the OC (overload, overcurrent, short circuit) signal output pin for the IGBT transistor, and the fault signal is returned to the CPU by an external optocoupler.
Figure 3 shows the U-phase drive circuit composed of PC923, PC929, and the post-amplifier.
The operation of the PC929's internal IGBT protection circuit is as follows: Under normal conditions, whether the inverter is in standby or running mode, pins 2 and 3 receive pulse signal current, and pin 11 successively generates +15V and -7.5V output drive voltage signals. At this time, pin 8 (FS) of the PC929 is always at a high level. When an abnormal current flows through the driven IGBT (such as more than twice the rated current), the IGBT's conduction voltage drop rises rapidly, causing the voltage at pin 9 to reach the fault alarm threshold (7V). The PC929's internal IGBT protection circuit is activated, the positive excitation voltage output at pin 11 decreases, causing the IGBT's conduction current to decrease. At the same time, it controls the transistor Q3 inside pin 8 to conduct, outputting a low-level OC fault signal, which is sent to the CPU via an external optocoupler. The CPU then implements protection shutdown and other actions based on the overcurrent situation.
Table 1. Resistance values (kΩ) of each pin on the output side of PC923 and PC929
During power-on testing of the power supply/driver board under separate repair, because pins 9 and 10 of the PC929 are disconnected from the IGBT module, pin 8 immediately reports an OC fault signal upon receiving an operating signal, and the output pulse voltage of pin 11 is also suppressed by the internal IGBT protection circuit, making it impossible to measure the operating status of the PC929. Appropriate measures need to be taken to disable the voltage drop detection function of the PC929, forcing the circuit to operate normally, thus facilitating testing.
III. Intelligent Driver IC – HCPL-316J (A316J):
Figure 4 shows the internal structure block diagram and pin function diagram of HCPL-316J.
Figure 5 shows the internal circuit diagram of HCPL-316J.
Figure 6 shows the drive circuit composed of HCPL-316J.
Figures 4 and 5 show the internal structure and schematic diagram of the A316J, respectively. The AJ316 has an output current of 2.5A, capable of directly driving a 150A/1200V IGBT. As a dedicated driver chip, its functions are nearly complete, and its peripheral circuitry is relatively simple. The input-side internal circuitry uses digital gate circuits with high impedance, eliminating the need for a large signal source current. It includes an undervoltage lockout output circuit and an IGBT protection circuit; it also includes two optocouplers for the input pulse signal and the output OC signal; it features fault-based drive pulse blocking and fault reset control functions, enabling automatic shutdown and automatic reset control in conjunction with the CPU.
As shown in Figures 4 and 5, the A316J internally uses the optical transmission channels of two optocouplers as the dividing points, separating the input-side circuit and the output-side circuit. Pins 1 and 2 are the positive/negative signal input terminals for VIN+ and VIN-, respectively. LED1, along with the relevant input-side and output-side circuits, constitutes the pulse signal transmission circuit. The input signal is transmitted to the output-side circuit via the gate circuit through LED1 (optocoupler). The optical signal received on the output side is then amplified by the controlled amplifier circuit and output from pin 11 to drive the IGBT module. The anode and cathode of LED1 are led out from pins 7 and 8, respectively, to facilitate the connection of an external fault protection circuit to cut off the transmission of the pulse signal. However, in conventional applications, pin 7 is usually left floating, and pin 8 is directly connected to the input-side signal (power) ground, forming a signal pass-through loop.
The internal output stage circuit is a push-pull output circuit, with a composite amplifier ensuring high current output capability. In the actual circuit, the power supply terminal 13 of the control circuit and the power supply terminal 12 of the output stage amplifier are also shorted and connected to the positive terminal of the power supply to the drive circuit. Pins 9 and 10 are connected to the negative terminal of the power supply, and the power supply voltage range is 15-30V.
The overload protection of the IGBT in the drive circuit is not achieved through current sampling—using a series current sampling resistor or a current transformer—but rather by determining whether the IGBT is in an overcurrent state based on the on-state voltage drop. When operating below the rated current, the IGBT voltage drop is no greater than 3V. When the operating current reaches twice the IGBT's current, the voltage drop will rise to over 7V. In this case, a protective shutdown should be initiated.
LED2 (optocoupler), together with the related circuits on the input and output sides, constitutes the IGBT voltage drop detection circuit, the IGBT module OC signal alarm circuit, and the fault reset circuit. Pin 14 is the input pin for the IGBT voltage drop signal (IGBT overcurrent detection signal), and pins 14 and 16 are connected in parallel to the collector and emitter of the IGBT via external components. Under normal operating conditions, the IGBT protection circuit does not activate, LED2 is in the off state, and the output Q of the internal RS flip-flop on the input side remains at a low level, having no control effect on the signal input path of LED1. Simultaneously, the internal DMOS transistor at pin 6 is in the off state due to lack of operating bias, and pin 6 (module OC signal output pin) is in a high-impedance state (high level), and the circuit operates normally. When the load is too heavy, the drive circuit itself malfunctions, or the IGBT suffers an open-circuit damage, when pin 14 detects a voltage drop of over 7V during IGBT conduction, the internal IGBT protection circuit activates. The internal power output circuit at pin 11 is first blocked, LED2 conducts, the Q of the RS flip-flop becomes high, the pulse signal input gate circuit is blocked, and simultaneously, the internal DMOS transistor at pin 6 conducts, inputting a low-level OC signal to the CPU or the preceding fault signal processing circuit. When the RS flip-flop is triggered, it maintains a fault-locked state, the transmission path of LED1 is cut off, and there is no drive signal output. When pin 5 of the AJ316 (reset signal input pin) receives a low-level reset signal (usually output by the CPU), the RS flip-flop is reset, and the pulse signal transmission channel formed by circuits such as LDE1 is reopened. Pin 15 is high-level when the OC fault signal is output, and can also be used with external circuits for fault alarms, etc. In general circuits, pin 15 is left unused.
The OC fault signal, power supply undervoltage signal, and pulse input signal determine the output state of the AJ316. The push-pull output circuit has an interlock function to ensure that the upper and lower transistors do not conduct simultaneously. When the power supply voltage drops below 12V, to avoid IGBT under-excitation leading to circuit failure, the internal undervoltage protection circuit is activated, forcing the lower DMOS transistor of the push-pull output circuit to conduct, pulling the drive pulse output terminal low, and cutting off the IGBT. During the valid pulse input signal period, if the IGBT protection circuit detects an abnormal increase in the IGBT's voltage drop, the protection circuit is activated, turning off the upper Darlington transistor of the push-pull output circuit, and fault locking is implemented by the RS flip-flop. At the same time, the DMOS transistor with the smaller amplification factor in parallel with the lower transistor in the push-pull output circuit conducts first, slowly releasing the charge stored in the G and E junction capacitance of the IGBT through the external trigger circuit, causing the IGBT to soft turn off. This avoids excessive Ldi/dt formed by the distributed inductance of the main circuit, which could easily cause the IGBT to exceed the safe operating area and be damaged.
The measurement and judgment of the A316J driver IC are shown in the table below.
Table 2 shows the resistance values of each pin of the A316J (measured using an MF47 multimeter in the 1k range).
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964 ) . We apologize for any inconvenience.
