Published:2011/7/26 1:21:00 Author:Li xiao na From:SeekIC
Design by G. Gerards
More design thoughts
The transformer for the project should be a toroidal type with a primary of 230 V and two 12-V secondary windings. Readers in countries with 110 V, 117 V or 127 V mains voltage are, of course, advised to use a matching 200-watt transformer. If you are lucky to have an old toroidal transformer lying around in a drawer or a junk box, it should not be too difficult to ’retro-fit’ two 12-V windings. Simply wind ten turns of litze wire around the core and connect the primary to the mains. Measure the voltage across your new winding and then calculate how many turns you need to get at 12 V At an output power of 200 watts, the average current will be about 10 A, so the cross-sectional area (c.s.a.) of the litze wire you’re using should be 1.5 mm2 or greater.
It is vital that the two 12-volt windings have exactly the same number of turns. If there is a difference of just one turn then the transformer core will saturate the instant the 12-volt battery is connected, causing the regulator to ’hang’ in shutdown mode. The sense direction) of the windings is equally important. Before installing the transformer, connect the ends of the two 12-volt windings in series and apply 230 Vac to the primary. You should measure 24 Vac across the free ends of the secondaries.
The FETs used in the circuit can handle up to 72 A at 55 V and are marked by an Ro-S(ON) of just 12Ω. Of course, other types may be used provided you are sure they can handle at last 40 A at 40 V and have an RD-S(ON) not exceeding 50 mΩ. Usually, power FETs may also be connected in parallel, but please make sure each one gets its own gate resistor. The parallel configuration is of interest if you wish to configure the inverter for output powers greater than 200 watts. In that case, the current limiter has to be adapted, which is easiest done by using a smaller value for shunt R8 and/or by modifying voltage divider R16-R17.
Ordinary bulbs and halogen (flood-) lights are sure sources of trouble with most power inverters. Both present a very low ’cold’ resistance, causing the inverter to reduce its output voltage or even actuate the shutdown. The result is a lock-up with insufficient voltage to heat up the filaments to their normal operating temperature. Fortunately, the 200-watt version of the inverter described here should be capable of turning on lamps of up to 150 watts without problems. Should problems arise, the value of capacitor C6 may be increased — but not to any extent because the ability of the circuit to withstand short-circuits may well suffer. Using C5 it is also possible to increase the soft-start time considerably, or do without it altogether. That, in all likelihood, is the safest solution.
Comparator IC1 monitors the battery voltage and ambient temperature and compares its measured results with the 5-V reference voltage from the 3526. The two open-collector outputs pull the shutdown control input (pin 8) to ground in case of an error. The PTC used determines the switch-off temperature. Depending on the exact type in your circuit. R6 may need slight red-imensioning. Early Aixcom prototypes of the inverter used a D901-D60-A40 from Epcos (trip temperature 60 degrees C). However, it should also be possible to use a temperature switch of 60 to 80 degrees C or a temperature fuse of 90 degrees C. Although the latter component is extremely cheap at just a few pence, you’ll need to exchange it when it has ’gone off’.
Provided a large enough heatsink is used, a simple wire link may be used instead of the PTC. The voltage monitor switches off at about 12 volt and this may be adapted to suit other levels by changing Rl and R5. On the comparators, R2 and R4 define an amount of hysteresis that prevents the power inverter from switching itself on again after a fault condition. After switching on, the reference voltage rises slowly as determined by the charge time of C2, hence the monitors are only activated a few seconds later.
Car batteries supply dangerously high currents. To prevent the inverter going up into flames and causing a fire, you must protect it with a car fuse of between 25 A and 35 A. The 230 Vac output voltage is also very dangerous even if it is generated by means of a battery.
Reprinted Url Of This Article: http://www.seekic.com/blog/project_solutions/2011/07/26/Simple_l2V_to_230V_Power_Inverter__A_mobile_power_outlet_(3).html
Print this Page | Comments | Reading(776)
Author:Ecco Reading(30212)
Author:Ecco Reading(3463)
Author:Ecco Reading(3183)
Author:Ecco Reading(3664)
Author:Ecco Reading(5235)
Author:Ecco Reading(3249)
Author:Ecco Reading(3391)
Author:Ecco Reading(3531)
Author:Ecco Reading(3937)
Author:Ecco Reading(3709)
Author:Ecco Reading(3678)
Author:Ecco Reading(3715)
Author:Ecco Reading(6029)
Author:Ecco Reading(3694)
Author:Ecco Reading(4480)