SURF PI 555 QUESTION

[daverave]

I want to use a 15v regulator to the 555 oscillator chip and 18v to the coil but when i tried this the coil drive was badly affected and mosfet draw very high current and the 7660 and 555 chips were damaged...what can i do to get around this problem cause i need to regulate the voltage to the 555 chip ???????

[WM6]

Check pulse length (by changing 555 supply voltage you change its pulse parameters too).

[Davor]

Supply voltage of 7660 is limited to under 11V. LT1054 is the same thing, but runs up to about 15V.

[Qiaozhi]

Supply voltage of 7660 is limited to under 11V. LT1054 is the same thing, but runs up to about 15V.

ICL7660 has an operating voltage range of +1.5V to 10.0V, and ICL7660A has a range of 1.5V to 12.0V.
The absolute maximum voltages are 10.5V and 13.0V respectively.
These device also have a tendency to curl up and die if these limits are exceeded, which is why the MPP uses an LT1054.

The LT1054L has an operating voltage range of 3.5V to 7.0V, and the LT1054 has a range of 3.5V to 15.0V.
Absolute maximum values in this case are 7.0V and 16.0V respectively.

[daverave]

im using the surf pi so the ICL 7660 is regulated at 5v...but its the 555 which is the problem as i regulated it at 15v and higher voltage to the coil then as i said the current consumption went up big time and mosfet was burning hot and the ICL 7660 and 555 were destroyed and one of the clipping diodes went low resistance...it was like the mosfet was not being switched off correctly.

[Qiaozhi]

im using the surf pi so the ICL 7660 is regulated at 5v...but its the 555 which is the problem as i regulated it at 15v and higher voltage to the coil then as i said the current consumption went up big time and mosfet was burning hot and the ICL 7660 and 555 were destroyed and one of the clipping diodes went low resistance...it was like the mosfet was not being switched off correctly.

In that case I think I can see the problem.
The MOSFET gets turned off when the 555 output goes high, but you've restricted the voltage supply to 15V. Since the MOSFET is connected to 18V, this leaves a 3V difference between the gate and source of the MOSFET. In other words, the MOSFET is permanently turned on. No wonder it got hot!

[daverave]

Hi Qiaozhi

is there a way around this problem ????

[Teleno]

Hi Qiaozhi

is there a way around this problem ????

By changing the voltage of the 555 to 15V you've also set the gate-sorce voltage that dives the MOSFET to 15V. This decreases the on-resistance of the MOSFET, which in turn increases the current. If the MOSFET current is not limited (for example, using a source resistor) then its current increases with the on-time time as a ramp, which can be catastrophic. Limiting the MOSFET current is essential if you don't dig smoke.

By th way, the 555 can also be configured as a negative voltage generator instead of the ICL7660 or the LT1054.

[Qiaozhi]

Hi Qiaozhi

is there a way around this problem ????

Have a look at the Hammerhead schematic. The 555 timer is running from a 5V supply, and the MOSFET is connected to the battery.
Basically, you will need to add a transistor between the output of the 555 and the MOSFET to invert the signal, and also reconfigure the 555 to invert the On-OFF pulses to compensate.

[kt315]

Qiaozhi, if you mean HH first revision so the 555 is running from batt directly. or... what HH revision you meant?

[junkhunter]

i tryed a voltage regulator project went crazy didnt work propley

[Qiaozhi]

Qiaozhi, if you mean HH first revision so the 555 is running from batt directly. or... what HH revision you meant?

Have a look at the attached HH schematic (D1). The 555 is connected to -5D, and the coil is connected to -VB.

Of course, the HH uses +VB as ground, whereas the Surf-PI uses -VB as ground. Therefore, you'll need to swap the transistor polarities around in order to use a PMOS to switch the coil.

[kt315]

you are right George, my mistaken. forgot in surf is P channel one in HH N channel mos-fet.

[chemelec]

The LT1054L has an operating voltage range of 3.5V to 7.0V, and the LT1054 has a range of 3.5V to 15.0V.
Absolute maximum values in this case are 7.0V and 16.0V respectively.

Another Option: The ICL7662 is good up to 20 Volts.

[daverave]

i appreciate your advice George with the hammerhead design to get around the problem but ive had no luck even getting the coil drive to work on the hammerhead which i made over a year ago...similar problem excessive current being drawn and mosfet over heating...which is another one of my project problems maybe with the surf pi i will just have to be happy with 16v to the coil.