I want to drive a power ignition IGBT (IRGB14C40L), and for this a driver MC33153 has been chosen. I have several questions about my supposed schematics, shown below: Ignition coil driver

0) This design will (allegedly) drive an automotive spark plug;

1) MC33153 datasheet tells us, that it's better to use separate turn-on (R1) and turn-off (R2) resistors, later one with diode (D1). For resistor values my calculations are based on IGBT datasheet: it tells that maximum peak current through Gate should not exceed 10 mA. So to be on the safe side R1 should be 1.5k Ohm. But how to choose D1?

2) How to choose value and type of C1 decoupling capacitor? I guess it should be physically located as close to Vcc and Vee pins as possible?

3) Datasheet of IGBT shows an internal resistor about 20k, which connects Gate to Emitter. I guess because of this, I don't need an external one to keep Gate low in case of floating input, am I right?

up vote 1 down vote accepted

1) The continuous gate current according to the specs of the IGBT is 1 mA, the 10 mA is allowed in pulses of 1 ms with 100 Hz frequency. This makes me a bit hesitant to put 8 mA or so as with your suggested set-up. I'd propose a maximum of 5 mA, or R1 = 2.7 kOhm.
For faster discharge you could take R2 = 10 kOhm. For D1 you'd need a really fast switching diode with a low reverse recovery time.

2) In decoupling switching phenomena from the supply you could take a tantalic capacitor for C1. Make sure to obtain and properly read the data sheet in order to select the right series resistor, 1 uF should do it.

3) Yes, and also the driver has a 100..200 kOhm pull-down resistor that would act the same, although I'm not sure when you suspect the gate to 'float', except for when the circuit is switched off.

Regarding the resistor in series to a tantalum: Tantalum capacitors have an extremely good high-frequency behavior and very low 'effective series resistance' (ESR) and are therefore excellent candidates to absorb disturbances due to switching. However, depending on the voltage and frequencies of the disturbances, the low ESR can lead to quite high compensation currents which can destroy the tantalum through overheating.
Once I also wasn't aware of this problem and repeatedly blew out the power stage of an experimental inverter that I've been working on. We repeatedly found a blown tantalum after the failure, started to actually read the specs and found the recommendation to apply series resistors.

  • 1) IGBT datasheet for all example circuits shows 1k gate resistor, is that because transistor is positioned as logic level, and driving voltage supposed to be 5V? 2) You mean capacitor datasheet? But how I should know, that tantalum capacitor is required, not aluminum, for example? And frankly speaking, I've never heard that I need a series resistor with decoupling cap... I'm a total newbie, however :) Thanks a lot! – Zhenek Jun 9 at 9:06
  • If you're a 'newbie' as you call yourself, you're not supposed to know anything about that, so I commend your efforts. I included an explanation of external tantalum series resistors in my answer. – HarryH Jun 9 at 9:19
  • 1) The driving voltage in your circuit is 12 V, not 5 V. – HarryH Jun 9 at 18:42
  • Thanks! Regarding question 1, I understand that I'm driving the circuit from 12V. I was just curious why manufacturer of IGBT placed 1k gate resistor in the datasheet without mentioning circuit driving voltage, at least directly. – Zhenek Jun 9 at 20:43

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