This page describes how to drive low impedance injectors with GenBoard/VerThree
There are different ways to drive low impedance (peak and hold) injectors:
- recommended: series resistor
- PWM-ing: turning voltage on / off across the injector, with a certain "duty (percentage)"
With series resistor, 30V unidir transient diode (high-voltage) flyback is mostly used.
With 30V unidir transient diode (high-voltage) flyback, the PWM parameters MUST BE:
- PWM peak time: 25.5msec
- PWM duty: 100%
This page is about PWM-ing. PWM-ing is not popular at all, because
- the low impedance injectors are around 1000-1200cc (a variaty of 100-727cc/min high-Z injectors are available and 1600cc that can be used as high-Z also)
- the 30V unidir transient diode (high-voltage) flyback that provides fast injector current rampdown and injector closing MUST NEVER be used with injector PWM-ing.
Warning
GenBoard/Manual/DDFlyback is very important for any injector setup.
When PWMing is configured, the low voltage flyback is the only option. The high voltage flyback will fry (itself and the FETs at least). (while the 20V flyback will always fry, for some injectors or with appropriate series resistor there can be a narrow operational range for the 6V8 flyback: it takes expertise to configure it, simply don't risk it. If set up bad it will fail at the worst possible time, at max power.).
PWM-ing is done as:
- injector is switched on for an amount of time (say 1 msec, configurable), this is the peak period. This allows fast injector-opening.
- injector is switched on an off with a given duty (say 40%, configurable, and depends on VBatt) at a given period (normally 64 usec). This holds the injector open without stressing it with too much current.
- injector is switched off after the commanded injector pulsewidth (same as for non-PWMing setup).
GenBoard/VerThree was designed so all 8 injection banks can be PWM-ed. It is achieved by PWM-ing OC0 with the given duty, and turning the PORTA pins IN/OUT-low/OUT-hi.
Without PWM-ing (for highZ injectors, or with series resistors) the common setup is to drive the insulated logiclevel FETs (see PowerSwitcher) from the AVR's pin, with 1k gate resistor (the FETdriver is replaced by simple bypass wire).
good to know for v3.0 v3.1 v3.2
- v3.0 : PWMing kit had to be ordered separately. FETdriver supply must be 12V_F, not 5V. Use D6 for 12V_F to MC34151D again: this is very important: MC34151 does not work from 5V, you'll need to select the 12V_F option on v3.0. Connect 1 and 2 at SJ1. To be sure, measure supply voltage of the FETdriver.
- v3.1 : everything needed for PWMing was in the rescue1 kit. 2 MC34151D FETdrivers were onboard, 2 in the rescue kit.
- v3.2 : everything required for PWMing is onboard, assembled in the picknplace run with 4xMC33151D FETdrivers. SIL5 R-network NOT needed, as 8 individual resistors are used instead (picknplaced). Therefore the first 3 requirements in the next section are satisfied, just verify them (shouldn't be any problem). Note that R154 10kOhm (marked 103) was accidentally left out from the picknplace, so some board were shipped without it before 2004.Oct.30. It's hard to notice, because its effect is only for a few millisec after the processor boots (before it switches the OC0 pin to output). Still recommended to solder it (at next maintenance, no need to rush to the car).
PWM-ing requires
- That FETdrivers are installed (see notes above)
- The R network (under the onboard MAP sensor) is populated (optionally 4k7..10k resistors between OC0 and all of the used injector control pins)
- It is recommended to pull the OC0 signal high with a 10k pullup resistor, R154(under the AVR, on the bottom side). This ensures that injectors are turned off when the AVR boots (pins are input).
- MY_CONF += -D FETDRIVER_INVERTING is defined in my_make (since the MC34151D FETdrivers are inverting)
- PWM parameters are configured (InitialConfig) according to the injector. PWM-duty 30% at 14V (60% at 6V) and 1024 usec peak-time can be good starting values for many setups (but ask if unsure)
- low-voltage FlyBack is used (DR, R=0) because FlyBack will activate each time the injector voltage is switched off during the PWM-ing phase (eg. 100 times for a 6.4ms injector pulsewidth!!!). With the high-voltage flyback this will be much heat in the box, not good.
HW notes
We use MC33151D or MC34151D (inverting) and R154 OC0 pullup under AtMega.
The IXDN404SI (noninverting) and R153 OC0 pulldown under AtMega
should work, but not supported.
- 2x R-network SIL5 (4+1 pin 2k2..10k) throughole (usually yellow)
Jason's debug session:
- Try to measure input current (short D6 with your DVM measuring current in 2A or 20A setting)
- 14 mA
- Check voltage drop across D6 with DVM diode-mode when the board is powered off:
- 1.2V
- C20, C24 0.1 .. 1uF. The FET is about <1nF, so 100 nF will drop 1/100 of the voltage when the gate is suddenly switched on. 220nF is installed by our standards